Automatic shift control system for automatic transmission

ABSTRACT

An automatic shift control system for a fluid controlled automatic transmission for a vehicle including a manual valve having a first position for establishing a relatively high forward drive ratio and a second position for establishing a relatively low forward drive ratio, a shift valve for controlling a plurality of fluid passages leading to brake bands and clutches from the manual valve to control the operation of the brake bands and clutches, and a solenoid for controlling the operation of the shift valve so that, in the first position of the manual valve, a low and a high forward drive ratio are obtained respectively, depending on the energization and de-energization of the solenoid, while in the second position of the manual valve, a low and a high forward drive ratio are obtained respectively which is dependent on the de-energization and energization of the solenoid.

United States Patent Ito et al. [451 Mar. 21, 1972 541 AUTOMATIC SHIFTCONTROL 3,433,101 3/1969 Scholl et al. ..74/866 EM F A T AT] 3,505,9094/1970 Maurice ig g gi 0M C 2,926,543 3/1960 l-loldeman et al ..74/86972 Inventors: Shin Ito; Seitoku Kubo; Takakazu Mol'i, PrimaryExaminer-Arthur McKeOfl a of Toyota, Japan Att0meyCushman, Darby &Cushman [73] Assignee: Toyota Jidosha Kogyo gahushjltililisha, [57]ABSTRACT Toyomshl Japan An automatic shift control system for a fluidcontrolled auto- [22] Filed: June 2, 1970 matic transmission for avehicle including a manual valve having a first position forestablishing a relatively high forward [2]] Appl' 42753 drive ratio anda second position for establishing a relatively low forward drive ratio,a shift valve for controlling a plurality 30 Foreign Application p i i Dm of fluid passages leading to brake bands and clutches from the Oct.18, 1969 Japan ..44/834l1 [52] U.S. Cl ..74/866, 74/867, 74/335, 74/752D [51] Int. Cl ..B60k 21/00, F 16h 5/06, F 16h 5/42 [58] Field of Search..74/865-868, 863, 74/864, 869

[56] References Cited UNITED STATES PATENTS 3,494,223 2/1970 Mori..74/869 X SH/FT CONTROL manual valve to control the operation of thebrake bands and clutches, and a solenoid for controlling the operationof the shift valve so that, in the first position of the manual valve, a

'low and a high forward drive ratio are obtained respectively,

depending on the energization and de-energization of the solenoid, whilein the second position of the manual valve, a low and a high forwarddrive ratio are obtained respectively which is dependent on thede-energization and energization of the solenoid.

9 Claims, 27 Drawing Figures TRANSM/SS/ON PATENTEDMARZI lsrz 3.650.161

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PATENTEDMARZI I972 3,650,161

sum user 15 AUTOMATIC SHIFT CONTROL SYSTEM FOR AUTOMATIC TRANSMISSIONBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to automatic transmissions for vehicles and more particularly toa combined electrical and hydraulic control system for such an automatictransmission.

2. Description of the Prior Art Conventional fluid controlled automatictransmissions employing therein an electrical control system for theshift signal control have been defective in that an unsatisfactory shiftcontrol results from trouble occurring in the electrical control systemand it is no more possible to drive the vehicle at a suitable speedratio for the driving condition at that time.

SUMMARY OF THE INVENTION With a view to overcome the above defect, it isa primary object of the present invention to provide improvements in theelectrical and hydraulic control systems in such automatic transmissionso that, in the event of trouble occurring in the electrical controlsystem, a shift lever disposed adjacent to the driver's seat may besuitably manipulated to select a speed ratio suitable for the drivingcondition, thereby to ensure a comfortable drive. In a preferredembodiment of the present invention, the shift lever is movable in fourdirections within two parallelly arranged guide slots so as to beselectively moved to one of six positions in the forward range. One ofthe two parallelly arranged guide slots is similar to that provided forconventional automatic transmissions and serves for the automatic shiftrange. The other guide slot serves for the semiautomatic shift range andmanipulation of the shift lever within this slot enables the vehicle torun at a speed ratio according to the drivers preference. Thesemiautomatic shift range which will be described in detail later iscontrolled independently of the electrical control system in response tothe manipulation of the shift lever and is not affected by any troublewhich may occur in the electrical control system. The provision of atransmission having six forward positions each giving a different shiftrange can thus realize a drive which is much wider in variety thanheretofore. To this end, the shift lever system, the electrical controlsystem and the hydraulic control system must be greatly modified.

This invention relates to improvements in the electrical and hydrauliccontrol systems in such an automatic transmission. In accordance withthe present invention which attains the above object, there is provided,in a fluid controlled automatic transmission for a vehicle having ahydraulic torque converter, a gear unit, frictionally engaging means foraccomplishing the selective meshing engagement of the gears in said gearunit, servo means operatively associated with said frictionally engagingmeans for producing ratio changes by selectively actuating saidfrictionally engaging means, and a hydraulic actuating circuitconnecting said servo means to a source of fluid pressure, an automaticshift control system comprising a manual shift range setting valve meanshaving a first position for establishing a relatively high forward driveratio and a second position for establishing a relatively low forwarddrive ratio, shift valve means disposed in a plurality of fluid passagesconnecting said manual shift range setting valve means with said servomeans for said frictionally engaging means to selectively allow andinterrupt the flow of fluid through said fluid passages so as to therebycontrol the operation of said frictionally engaging means, and means forcontrolling the operation of said shift valve means so that a highforward drive ratio is given when the said shift valve means is urged toone position by said shift valve control means in the first position ofsaid manual shift range setting valve means, while in the secondposition of said manual shift range setting valve means, the sameposition of said shift valve means gives a low forward drive ratio.

In accordance with the present invention, there is further provided anautomatic shift control system of the above character in which, whensaid manual shift range setting valve means is in the first position, alow and a high forward drive ratio are obtained respectively, dependingon the energization and de-energization of said shift valve controlmeans, while when said manual shift range setting valve means is in thesecond position, a low and a high forward drive ratio are obtainedrespectively depending on the de-energization and energization of saidshift valve control means.

Other objects, features and advantages of the present invention willbecome apparent from the following detailed description taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of anautomatic transmission according to the present invention.

FIG. 2 is a schematic sectional view of a transmission unit to which thepresent invention is applied.

FIG. 3 is an enlarged sectional view taken on the line A-A in FIG. 2with parts cut away to show in detail the relation between an idler gear(not shown in FIG. 2) and the sun gear and planet pinion.

FIGS. 4 through 8 are diagrammatic views illustrating the operation of ahydraulic actuating circuit when the present invention is adapted to athree-forward speed automatic transmission in which the hydraulicactuating circuit is shown in its N position, D position 3rd speed, Dposition 2nd speed, L position 1st speed and L position 2nd speed,respectively.

7 FIG. 9 is a graph showing how the line pressure controlled by thehydraulic actuating circuit in the D position varies relative to ther.p.m. of the output shaft.

FIG. 10 is a graph showing how the line pressure controlled by thehydraulic actuating circuit in the D or L position varies relative tothe r.p.m. of the output shaft.

FIG. 11 is a perspective view of a shift lever system employed in thepresent invention.

FIG. 12 is a sectional view taken on the line 8-3 in FIG. 11 to show theinternal structure of the shift lever system.

FIG. 13 is a block diagram of a shift signal control system preferablyemployed in the automatic transmission of the present invention.

FIGS. 14a and 14b are a side elevational view and a front elevationalview, respectively, of an r.p.m. detector preferably used in the shiftsignal control system.

FIG. 15 is a block diagram showing the structure of a digital-analogconverter preferably used in the shift signal control system.

FIGS. 16a, 16b and 16c are graphic illustrations of the operatingvoltage waveforms appearing in the digital-analog converter shown inFIG. 15. 1

FIG. 17 is a circuit diagram showing the structure of a throttleposition circuit preferably used in the shift signal control system.

FIG. 18 is a circuit diagram showing the structure of a discriminatingcircuit and an associated feedback circuit preferably used in the shiftsignal control system.

FIG. 19 is a chart showing the relation between a signal representativeof the output shaft r.p.m. and a signal representative of the throttleposition to illustrate the shift ranges according to the presentinvention when the shift lever is in the D or D position.

FIG. 20 is a chart showing the relation between the output shaft r.p.m.signal and the throttle position signal to illustrate the shift rangesaccording to the present invention when the shift lever is in the Lposition.

FIG. 21 is a circuit diagram showing the structure of a gate circuitpreferably used in the shift signal control system.

FIG. 22 is a shift diagram showing one example of the shift ranges whenthe shift lever is in the D or D, position.

FIG. 23 is a shift diagram showing one example of the shift ranges whenthe shift lever is in the L position.

FIG. 24 is a block diagram of a modification of the 1-2 shift system inthe shift signal control system shown in FIG. 13, the

modification employing only one 1-2 shift discriminating circuit in lieuof two.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

Referring to FIG. 1, the constituent of the automatic transmissionembodying the present invention may be broadly divided into a shiftcontrol system including a source of electrical power supply, shiftlever means and shift computing circuits, a transmission unit includinga hydraulic torque converter, a speed changing gear unit andfrictionally engaging means, and a hydraulic actuating system includingfluid passages, shift valves for switching over the fluid passages uponreceiving a signal from the shift control system, and a source of fluidpressure for actuating the frictionally engaging means. These componentswill be described in detail hereinafter.

STRUCTURE OF THE TRANSMISSION A torque converter automatic transmissionhaving three forward speeds and one reverse speed as shown in FIG; 2will be taken as a typical example of an automatic transmission. In FIG.2, the structure of such a fluid controlled automatic transmission isschematically shown.

A torque converter unit includes a pump impeller 2 directly connected toa crankshaft 1 of an engine. The power developed by the engine istransmitted from the pump impeller 2 to a turbine impeller 3 through themedium of hydraulic fluid, and the fluid is returned to enter the pumpimpeller 2 again by being guided by a stator 4. A rotational force canbe continuously derived from a turbine shaft 5 by the repeated operationof the above fluid flow. This rotational force is transmitted from theturbine shaft 5 to a gear unit disposed at the output side of the torqueconverter unit. As is commonly known, multiple disc clutch means 6 and 7and brake band means 21 and 22 are automatically controlled by fluidpressure supplied from associated servo means as required and cooperatewith a planetary gear mechanism to provide three forward speeds and onereverse speed."

The structure of the gear unit disposed at the output side of the torqueconverter unit will now be described. The turbine V impeller 3 isconnected to the turbine shaft 5 which acts as a power input shaft ofthe planetary gear mechanism. The turbine shaft 5 is splined to a drum24 for unitary rotation therewith. Disposed within the drum 24 is amultiple disc clutch 6 (hereinafter to be referred to as a front clutch)which is engaged by means of a piston 25 actuated by fluid pressure andthat is released by means of back-up springs. The drive plates of thefront clutch 6 are externally splined to engage the internally splinedportion of the drum 24, and the clutch discs are internally splined toengage the externally splined portion of a hub 26 so as to be lockedagainst free rotation. The hub 26 is internally splined to engage theexternally splined portion of an intermediate shaft 8. The clutch discsof a multiple disc clutch 7 (hereinafter to be referred to as a rearclutch) are internally splined to engage the externally splined portionof the front clutch drum 24 as shown so as to be locked against freerotation. Thus, the clutch discs of the rear clutch 7 rotate in unisonwith the front clutch drum 24. The driven plates of the rear clutch 7are externally splined to engage the internally splined portion of aclutch drum 27 of the rear clutch 7. The rear clutch 7 is engaged bymeans of a fluid pressure actuated piston 28 and disengaged when thefluid pressure applied to the piston 28 is released.

The intermediate shaft 8 which is splined to the hub 26 of the frontclutch 6 is connected at its rear end to an input sun gear 9. The rearclutch drum 27 is fixed to a reverse sun gear 10 by a suitable lockingmeans. The input sun gear 9 meshes with each gear 12 of a plurality of,for example, two or three planet pinions 11. The reverse sun gear 10mesheswith idler gears (shown in FIG. 3) which are each rotatablymounted on a pin 14 fixed at one end to a carrier 13, and the idlergears 15 in turn meshes with gears 16 of the planet pinions 11.

The rearmost gear 17 of each planet pinion 11 meshes with a gear 19mounted at the front end of an output shaft 18 of the transmission. Theplanet pinions 11 having the gears 16, 12 and 17 and the idler gears orpinions 15 are carried by the carrier 13 by means of pinion pins 20 and14, respectively. A brake band 21 (hereinafter to be referred to as arear brake band) encircles the carrier 13 for applying a brake to thelatter, and thus the carrier 13 can be fixed against rotation andallowed to freely rotate by fastening and releasing the rear brake band21. Similarly, a brake band 22 (hereinafter to be referred to as a frontbrake band) encircles the rear clutch drum 27 so that the rear clutchdrum 27, hence the sun gear 10 can be fixed against rotation and allowedto freely rotate by fastening and releasing the front brake band 22. Aone-way clutch 23 associated with the carrier 13 functions in a mannersimilar to the rear brake band 21 in low gear set forth hereunder.

With the above structure, three forward speeds and one reverse speed canbe obtained by selectively actuating the elements described above in thefollowing manner:

First speed The front clutch 6 and the rear brake band 21 are actuated.(However, when the transmission is driven from the engine, the rearbrake band 21 may not be actuated since the one-way clutch 23 isactuated to give the same result as that obtained with the actuation ofthe rear brake band 21. In this case, however, no driving force istransmitted from the output shaft 18 to the engine.) With the frontclutch 6 and the rear brake band 21 so actuated, the rotation of theturbine shaft 5 is directly transmitted to the input sun gear 9 throughthe front clutch 6. Due to the fact that the carrier 13 is lockedagainst rotation by the rear brake band 21, the pinion pins 20 are alsoheld stationary and the rotation of the turbine shaft 5 is transmittedfrom the gear 9 to the gears 12, thence through the gears 17 to the gear19 on the output shaft 18 in a speed reducing relation similar to thatof an ordinary gear train, thereby providing the first speed.

Second speed The front clutch 6 is kept actuated and the front brakeband 22 is actuated while releasing the rear brake band 21. Thus, theinput sun gear 9 is rotated in unison with the turbine shaft 5, but therear clutch drum 27, hence the reverse sun gear 10 is locked againstrotation by the front brake band 22. In this state, the rotation of theturbine shaft 5 is directly transmitted to the input sun gear 9, and thesun gear 9 urges the pinions 1 1 to rotate in a direction(counterclockwise) opposite to the direction of rotation (clockwise) ofthe turbine shaft 5. The planet pinions 11 rotating in this directiontend to rotate the idler gears 15 clockwise through the gears 16.However, due to the fact that the gear 10 meshing with the gears 15 islocked against rotation, the pinion pins 14 revolve clockwise around thegear 10. This revolving motion is imparted to the rotation of the inputsun gear 9 and the gear 19 carried by the output shaft 18 which gearsare coaxial with and rotate in the same direction as the turbine shaft5. Since the number of teeth of the gear 12 is selected to be greaterthan the number of teeth of the gear 17, the number of revolutions ofthe intermediate shaft 8 is greater than that of the output shaft 18. Inother words, the output shaft 18 is rotated at a reduced speed or secondspeed.

Third speed The third speed can be obtained by engaging both the frontand rear clutches 6 and 7. The input sun gear 9 and the reverse sun gear10 are rotated in unison and the whole planetary gear system isunitarily rotated so that the output shaft 18 is rotated at the rotatingspeed of the turbine shaft 5.

Reverse When reversing, the rear clutch 7 and the rear brake band 21 areactuated. The carrier 13, hence the pinion pins 14 and 20 are therebylocked against revolution, and the rotation of the turbine shaft 5 istransmitted through the rear clutch 7 to the reverse sun gear 10, thencethrough the pinions 15, 16 and 17 to the gear 19 mounted on the outputshaft 18 so that the output shaft 18 is rotated in the reversedirection.

HYDRAULIC ACTUATING SYSTEM The arrangement of a hydraulic actuatingsystem preferably used in combination with the automatic transmissionaccording to the present invention is diagrammatically shown in FIGS. 4through 8. Briefly, the hydraulic actuating system comprises a fluidpressure source 100 and a hydraulic actuating circuit 1 10. Thehydraulic actuating circuit 1 includes a manual valve 120, a l-2 shiftmeans 130, a 2-3 .shift means 135, a check valve 140 and fluid passages.The fluid pressure source 100 includes an oil pump 101, an oil strainer102, a pressure regulator valve 105, a relay valve 150, a check valve103, an oil cooler 104 and fluid passages. The fluid pressure source 100functions to supply fluid under pressure to the torque converter, to thegears for lubricating same and to the hydraulic actuating circuit 110.

The manual valve 120 is connected with a shift lever 601 (shown in FIGS.11 and 12) disposed adjacent to the drivers seat and takes one of the P,R, N, D D and L positions. Now, when the manual valve 120 takes the Nposition, a fluid passage 121 is closed and valve chambers 122 and 123are exhausted as seen in FIG. 4. At the D position of the manual valve120, the fluid passage 121 communicates with fluid passages 124, 125 and126 as seen in FIG. 5. The fluid passage 124 leads directly to a frontclutch servo chamber 6a, and the fluid passage 125 leads to the applyside 22a of a servo for the front brake band 22 through the l-2 shiftmeans 130, while the fluid passage 126 leads to a rear clutch servochamber 7a and to the release side 22b of the servo for the front brakeband 22 through the 2-3 shift means 135 and the check valve 140. The l-2shift means 130 includes a 1-2 shift valve element 131 and a solenoid132. One end (or the right-hand end as viewed in the drawing) of thevalve element 131 is abutted by a moving core 133 of the solenoid 132.When no current is supplied to the solenoid 132, the valve element 131is urged to its rightward position by a spring 131' engaging the otheror left-hand end of the valve element 131 so that the fluid passage 125communicates with a fluid passage 134 to supply fluid to the apply side22a of the servo for the front brake band 22 to apply the front brakeband 22. When current is supplied to the solenoid 132, the moving core133 urges the valve element 131 to the leftward position by beingactuated by the electromagnetic force of the solenoid 132 so that thecommunication between the fluid passages 125 and 134 is interrupted andthe fluid passage 134 communicates with a fluid passage 127 to beexhausted thereby releasing the front brake band 22. Similarly, the 2-3shift means 135 includes a 2-3 shift valve element 136 and a solenoid137. One end (or the righthand end as viewed in the drawing) of thevalve element 136 is engaged by a moving core 138 of the solenoid 137.When no current is supplied to the solenoid 137, the valve element 136is urged to its rightward position by a spring 136' engaging the otheror left-hand end of the valve element 136 so that the fluid passage 126communicates with a fluid passage 139 to force a check ball element 141of the check valve 140 towards the fluid passage 128 to block the fluidpassage 128. As a result, the fluid passage 139 communicates with afluid passage 142 to supply fluid to the rear clutch servo chamber 70and to the release side 22b of the servo for the front brake band so asto engage the rear clutch 7 and release the front brake band 22. Whencurrent is supplied to the solenoid 137, the valve element 136 is urgedleftward so that the communication between the fluid passages 126 and139 is interrupted and the fluid passage 139 communicates with apressure discharge port 139a to be exhausted.

In the first speed at the D drive range position or D position 1stspeed, both the solenoids 132 and 137 are energized and the front clutch6 is solely engaged by the supply of fluid to the front clutch servochamber 6a through the fluid passage 124. Accordingly, when thetransmission is driven from the engine, the one-way clutch 23 is engagedto lock the carrier 13 against rotation so that the first speed can beobtained. In this case, however, no driving force can be transmitted tothe engine from the output shaft 18 since a freewheeling conditionappears.

In the second speed at the D, drive range position or D, position 2ndspeed, the fluid passage 124 leading to the front clutch servo chamber60 is kept pressurized and the solenoid 132 for the l-2 shift valveelement 131 is de-energized with the result that the fluid passage 125communicates with the fluid passage 134 to supply fluid to the applyside 22a of the servo for the front brake band 22 to apply the frontbrake band 22. Thus, the second speed can be obtained.

In the third speed at the D, drive range position or D, position 3rdspeed shown in FIG. 5, the solenoid 137 for the 2-3 shift valve element136 is de-energized in addition to the previous de-energization of thesolenoid in the D position 2nd speed with the result that the fluidpassage 126 communicates with the fluid passage 139 to supply fluid tothe rear clutch servo chamber 7a to engage the rear clutch 7 whilereleasing the front brake band 22. Thus, the third speed can beobtained.

when the manual valve is urged to the D position shown in FIG. 6, thefluid passage 126 leading to the 2-3 shift means 135 is exhausted andthe fluid passages 124 and 125 communicate solely with the fluidpressure source 100. Accordingly, it is impossible to obtain the thirdspeed, regardless of the de-energizatiorr of the solenoid 137 for the2-3 shift valve element 136 and the first and second speeds can beachieved, depending on the energization and de-energization of thesolenoid 132 for the 1-2 shift valve element 131.

When the manual valve 120 is urged to the L position, the fluid passages125 and 126 are exhausted and the fluid passages 124 and 127 communicatewith the fluid pressure source 100. When, in this case, no current issupplied to the 1-2 shift solenoid 132 and the l-2 shift valve element131 takes its rightward position as seen in FIG. 7, the fluid passage127 communicates with a fluid passage 127 to supply fluid to the applyside 21a of a servo for the rear brake band 21. Thus, the front clutch 6is engaged and the rear brake band 21 is applied so that the first speedcan be obtained. The first speed in this case differs from the firstspeed in the D, position in that the rear brake band 21 is applied toprovide for transmission of the driving force from the output shaft tothe engine thereby permitting the application of engine braking. When,on the other hand, current is supplied to the l-2 shift solenoid 132 andthe l-2 shift valve element 131 is urged to its leftward position asseen in FIG. 8, the fluid passages 127 and 127 communicate with thefluid passage 134 and a pressure discharge port 134 and a pressuredischarge port 134a, respectively, with the result that fluid issupplied to the apply side 22a of the servo for the front brake band 22to apply the front brake band 22 while the rear brake band 21 isreleased. Thus, the second speed can be obtained.

When the manual valve 120 is moved to the R position, the fluid passages124, 125 and 126 become exhausted and the fluid passages 127 and 128thus communicate with the fluid pressure source 100. As a result, fluidis supplied to the rear clutch servo chamber 7a and to the apply side21a of the servo for the rear brake band 21 to engage the rear clutch 7and apply the rear brake band 21. Thus, the reverse drive condition forthe vehicle can be obtained.

It will be understood from the foregoing description that the hydraulicactuating system in the present invention is featured by the fact thatit comprises the combination of a novel hydraulic circuit arrangementand biasing means in the form of the springs 131 and 136' for biasingthe 1-2 shift valve element 131 and the 2-3 shift valve element 136 tothe rightward position in response to de-energization of the respectivesolenoids 132 and 137. The circuit arrangement of the hydraulicactuating system is such that, in the D position of the manual valve120, fluid pressure from the fluid pressure source 100 is supplied tothe front clutch servo chamber 6a for the front clutch 6 through thefluid passage 124, to the apply side 22a of the servo for the frontbrake band 22 through the fluid passage 125 and the 1-2 shift means 130,and to the rear clutch servo chamber 7a for the rear clutch 7 and to therelease side 22b of the servo from the front brake band 22 through thefluid passage 126 and the 2-3 shift means 135, respectively. In the Dposition of the manual valve 120, the fluid passage 126 leading to the2-3 shift means 135 is exhausted and the fluid passages 124 and 125communicate with the fluid pressure source 100, while in the L positionof the manual valve 120, the fluid passage 125 leading to the l-2 shiftmeans 130 is further exhausted and the fluid passage 127 communicatingwith the fluid pressure source 100 communicates with the fluid passage134 leading to the apply side 22a of the servo for the front brake band22 through the l-2 shift means 130 or with the fluid passage 127'leading to the apply side 21a of the servo for the rear brake band 21.By virtue of the above combination, even in the event of theinterruption of electrical power from its source to the shift signalcontrol system which determines the energization and de-energization ofthe solenoids 132 and 137, the manual valve 120 may be urged to the Lposition for obtaining the first speed, to the D position for obtainingthe second speed and to the D, position for obtaining the third speed.Further, in the L position of the manual valve 120, the fluid passage127 can communicate with the apply side 22a of the servo for the frontbrake band 22 and with the apply side 21a of the servo for the rearbrake band 21 through the l-2 shift means 130 depending on thede-energization and energization of the solenoid 132. Thus, the manualvalve 120 may be shifted to the L position while driving at high speedand the solenoid 132 may be energized so as to maintain the secondspeed, thereby preventing the overrunning of the engine.

Such a hydraulic circuit arrangement is quite advantageous in that, whentrouble occurs in the shift signal control system which controls thesupply of electrical signals to the solenoids or when the driver wishesa sporty drive with a variety of speed changes compared with thosecarried out on the basis of the shift points primarily set forth for theelectrical control system, the drive may turn off the switch connectingthe voltage source with the shift signal control system to cut off thesupply of power to the shift signal control system thereby rendering theshift signal control system inoperative, and may then urge the manualvalve to one of the L, D and D, positions by the shift lever so as toselect the desired speed ratio. In other words, the switch may be turnedon and off to select either driving under completely an automatic shiftcontrol or driving under a semiautomatic shift control as desired.

A second feature of the present invention resides in the fact thatcurrent is supplied to the solenoid 132 from the shift signal controlsystem upon shifting to the L position during the driving at high speedso that first-speed engine braking cannot be applied to the engine,thereby preventing the engine from an abrupt engine brake andoverrunning.

A third feature of the present invention resides in the fact that thesolenoids 132 and 137 are in the de-energized state during the drivingof the vehicle in the third speed gear. Therefore, it is unnecessary toconsider any electrical power consumption due to operation of thesolenoids as well as the undesirable generation of heat resulting in atemperature rise due to the current supplied to the solenoids.

Fluid pressure supplied to the servos, that is, line pressure iscontrolled by the pressure regulator valve 105. The pressure regulatorvalve 105 includes a valve spool 105' which is engaged at one or upperend by a spring 106. Fluid from the oil pump 101 is supplied through therelay valve 150 to a valve chamber 108 surrounding an upper portion ofthe valve spool 150'. In the D, position of the manual valve 120, thevalve chamber 108 is supplied with fluid via the fluid passages 121 and126 and the relay valve 150 having a valve spool 150' engaged by aspring 151. A valve chamber 109 surrounding a lower portion of the valvespool 105' is supplied with fluid via a fluid passage 134'. Thus, in theD, position of the manual valve 120 shown in FIG. 5, fluid pressuresupplied from the oil pump 101 is fed into an upper port 1500 of therelay valve 150 via the fluid passages 121 and 126. On the other hand,fluid pressure supplied from the oil pump 101 into a port 105b of thepressure regulator valve 105 is applied to a lower valve chamber 1500 ofthe relay valve 150. The fluid pressure fed into the upper port 1500 ofthe relay valve 150 cooperates with the spring 151 engaging the upperend of the valve spool 150' of the relay valve 150 to urge the valvespool 150' downwardly, while the fluid pressure applied to the lowervalve chamber 150a of the relay valve 150 through the port b of thepressure regulator valve 105 imparts an upward force to the valve spool150 of the relay valve 150. Since the fluid pressure imparted to theupper end of the valve spool 150 is equal to the fluid pressure impartedto the lower end of the valve spool 150, the downward force is strongerthan the upward force by an amount corresponding to the force of thepre-stressed spring 151 with the result that the valve spool 150 of therelay valve 150 is urged to a lower preset position. Therefore, the oilpump pressure is applied to the upper chamber 108 of the pressureregulator valve 105. Upon deenergization of the 1-2 shift solenoid 132,the 1-2 shift valve element 131 is urged to its rightward position withthe result that the fluid passage communicates with the fluid passage134 to supply fluid pressure to the lower valve chamber 109 of thepressure regulator valve 105 via the fluid passage 134'. In such astate, a low constant line pressure P is produced by the pressureregulator valve 105. This constant line pressure P is determined by theforce of the pre-stressed spring 106 and fluid pressure (pump pressure)in the chambers 108 and 109 acting upon the different cross-sectionalareas of the valve spool 105.

When the l-2 shift solenoid 132 is energized to urge the l-2 shift valveelement 131 to its leftward position, the fluid passage 134 communicateswith the fluid passage 127 to be drained and the lower valve chamber 109of the pressure regulator valve 105 is exhausted. In such a state, arelatively high constant line pressure P is produced by the pressureregulator valve 105 and is determined by the force of the prestressedspring 106 and fluid pressure (pump pressure) in the chamber 108 actingupon the different cross-sectional areas of the valve spool 105. It willthus be understood that, in the D, position of the manual valve 120, therelatively high constant line pressure P is produced by the pressureregulator valve 105 when the l-2 shift valve element 131 is urged to itsleftward position to provide the first speed, while the low constantline pressure P is produced by the pressure regulator valve 105 when thel-2 shift valve element 131 is urged to its rightward position toprovide the second and third speeds. FIG. 9 shows the variation in theline pressure produced by the pressure regulator valve 105 in the D,position of the manual valve 120 relative to the number of revolutionsof the output shaft and hence the vehicle speed. As will be seen fromFIG. 9, a step-down from the relatively high constant line pressure P tothe low constant line pressure P occurs in the D, position of the manualvalve 120 when the number of revolutions of the output shaft 18, hencethe vehicle speed is increased and the speed ratio is changed from thefirst speed to second. Generally, the l-2 shift point and 2-1 shiftpoint are variable depending on an engine torque responsive signal.Thus, the step-down from the constant line pressure P to the constantline pressure P varies as shown depending on the engine torqueresponsive signal.

The fluid passage 126 is exhausted in the positions of the manual valve120 except in the D, position. In those positions of the manual valve120, oil pump pressure supplied from the lower valve chamber a of therelay valve 150 to the upper valve chamber 108 of the pressure regulatorvalve 105 is reduced by an amount corresponding to the force of theprestressed spring 151 to appear as a pressure P which is called hereina reducing pressure. In the D position of the manual valve 120, fluidpressure is supplied to the fluid passage 125, while in the L positionof the manual valve 120, fluid pressure is supplied to the fluid passage127. Thus, as in the case of the D, position of the manual valve 120,fluid pressure is supplied via the fluid passage 134' or not supplied tothe valve chamber 109 of the pressure regulator valve 105, depending onthe position of the l-2 shift valve element 131. When fluid pressure isapplied to the valve chamber 109, a relatively low con-

1. In a shift control system for a fluid controlled vehicle transmissionhaving a hydraulic torque converter, a gear unit, frictionally engagingmeans for accomplishing a selective meshing engagement of the gears insaid gear unit, servo means operatively associated with saidfrictionally engaging means for producing ratio changes by selectivelyactuating said frictionally engaging means, and a hydraulic actuatingcircuit connecting said servo means to a source of fluid pressure, theimprovement comprising: a manual shift range setting valve means havinga first position for establishing a relatively high forward drive ratioand a second position for establishing a relatively low forward driveratio disposed in said hydraulic actuating circuit, a shift valve meansdisposed in said hydraulic actuating circuit between said servo meansand said manual shift range setting valve means having two positions toselectively pass and stop the fluid through said hydraulic actuatingcircuit to thereby control the operation of said frictionally engagingmeans, and an electrical shift valve control means for controlling saidshift valve means to be urged to one position of said two positions orto the other position, said shift valve means, when said manual shiftrange setting valve means is in the first position, supplying fluidpressure to said servo means so as to establish a high forward driveratio at said one position and a low forward drive ratio at said otherposition and, when said manual shift range setting valve means is in thesecond position, supplying fluid to said servo means so as to establisha low forward drive ratio at said one position and a high forward driveratio at said other position contrary to the case when said manual shiftrange setting valve means is in the first position.
 2. The shift controlsystem as claimed in claim 1 wherein said shift valve means comprises anelectrical operator and said means for controlling said shift valvemeans comprises means responsive to vehicle operating conditions forgenerating at least two electrical signals, at least a first and asecond discriminating circuit for comparing said electrical signals andproducing outputs when one of said signals exceeds the other, anelectrical gate for connecting either said first or said seconddiscriminating circuits to said electrical operator and means forcontrolling said gate associated with said manual range setting means.3. The shift control system as claimed in claim 2 wherein the means forgenerating two electrical means comprises a toothed disc of magneticmaterial securely mounted coaxially on the output shaft of said vehicletransmission and a coil located adjacent to the outer periphery of saidtoothed disc the axis of said coil being located on a line radial tosaid disc whereby a voltage having a frequency proportional to therotational speed of said output shaft is induced in said coil, and amovable contact mechanically connected with the carburetor throttle of asaid vehicle, a plurality of fixed contacts arranged to engage with saidmovable contact each of said fixed contacts connected through a separateresistance to a source of electrical power and a voltage tap lineconnected in common between said resistances and said power sourcewherein the movement of said carburetor throttle causes said movablecontact to engage a varying number of fixed contacts and thus to verythe output voltage on said voltage tap line proportional to the settingof said carburetor throttle.
 4. The shift control system as claimed inclaim 2 wherein each discriminating circuit has two input leads and saidelectrical signals are connected oppositely to the leads of said seconddiscriminating circuit with respect to their connections with said firstdiscriminating circuit so that each discriminating circuit produces anoutput when a different one of said electrical signals predominates theother signal.
 5. The shift control system as claimed in claim 2 whereinsaid means for controlling said gate includes an input lead to said gatesaid gate connecting said first discriminating circuit to saidelectrical operator in the absence of a signal upon said input lead andconnecting said second discriminating circuit to said electricaloperator in the presence of a signal upon said input lead.
 6. The shiftcontrol system as claimed in claim 5 wherein said means associated withsaid manual shift range setting means includes a source of electricalpower and a switch mechanically connected to said manual shift rangesetting valve means and electrically connected between said source ofelectrical power and said input leads, said switch being open when saidmanual shift range setting means is in said first position and closedwhen said manual shift range setting means is in said second position.7. The shift control system of claim 6 wherein each of saiddiscriminating circuits includes a feedback circuit connected betweensaid output lead of said comparator and said first input lead thereoffor adding a portion of the output signal produced by saiddiscriminating circuit to the input signal at said first input leadwhereby signals on said output lead are stabilized.
 8. In a fluidcontrolled automatic transmission for a vehicle having a hydraulictorque converter, a gear unit, frictionally engaging means foraccomplishing the selective meshing engagement of the gears in said gearunit, servo means operatively associated with said frictionally engagingmeans for providing ratio changes by selectively actuating saidfrictionally engaging means, and a hydraulic actuating circuitconnecting said servo means to a source of fluid pressure, an automaticshift control system comprising manual shift range setting valve meansresponsive to the position of a shift lever and having a first positionfor establishing a relatively high forward drive ratio and a secondposition for establishing a relatively low forward drive ratio, shiftvalve means disposed in said hydraulic actuating circuit between saidmanual shift range setting valve means and said servo means toselectively pass and stop the fluid through said hydraulic actuatingcircuit to thereby control the operation of said frictionally engagingmeans, means for generating a signal responsive to the throttleposition, means for generating a signal responsive to the r.p.m. of theoutput shaft, a plurality of discriminating circuits having their inputterminals connected to the outputs of said throttle position responsivesignal generator and said vehicle speed responsive signal generator,means including a solenoid for controlling the operation of said shiftvalve means, a gate circuit connected between the outputs of saiddiscriminating circuits and said solenoid for selectively applying theoutputs from said discriminating circuits to said solenoid, and switchmeans responsive to the position of the shift lever, said switch meanshaving a lead connected to said gate circuit for controlling theoperation of said gate circuit depending on the first and secondposition of the shift lever, in which a high forward drive ratio isprovided when said shift valve means is urged to one position by saidsolenoid in the first position of said manual shift range setting valvemeans, while in the second position of said manual shift range settingvalve means, the same position of said shift valve means provides a lowforward drive ratio.
 9. An automatic shift control system as claimed inclaim 8, in which, when said manual shift range setting valve means isin the first position, a low and a high forward drive ratio are providedrespectively depending on the energization and deenergization of saidsolenoid, while when said manual shift range setting valve means is inthe second position, a low and a high forward drive ratio are providedrespectively depending on the deenergization and energization of saidsolenoid.